1. Field of the Disclosure
The present application relates to a control apparatus for a hybrid vehicle including an internal combustion engine, an electric motor and a storage battery that supplies electric power to the electric motor.
2. Description of Related Art
Conventionally, a hybrid vehicle (hereinafter, also simply referred to as vehicle) travels while controlling an electric motor and an internal combustion engine such that the capacity of a chargeable and dischargeable storage battery is efficiently utilized for the purpose of improvement in the fuel consumption performance of the vehicle.
On the other hand, a repetitive change in an extremely large remaining amount of charge (hereinafter, also simply referred to as state of charge (SOC)) or extremely small remaining amount of charge of the storage battery accelerates the performance degradation of the storage battery. Therefore, the SOC of the storage battery is managed for the purpose of preventing the degradation of the storage battery. Specifically, the upper limit and lower limit of the SOC are prescribed, and a control apparatus manages the SOC such that the SOC does not go beyond the range (referred to as management range) between the upper limit and the lower limit.
That is, the control apparatus prohibits charging the storage battery when the SOC reaches the upper limit. At this time, electric energy that is generated as a result of regenerative braking is transformed into thermal energy in a friction brake device or an inverter or both, or the like, so energy originally recoverable and usable for propelling the vehicle is consumed uselessly. In contrast, when the SOC reaches the lower limit, the control apparatus forcibly charges the storage battery by using the output power of the internal combustion engine. As a result, fuel is consumed due to a cause other than propelling the vehicle. Therefore, causing the SOC not to reach the upper limit or the lower limit during traveling of the vehicle leads to effective improvement in the fuel consumption performance of the vehicle.
Incidentally, when the vehicle travels on such a downhill that the vehicle accelerates without using the torque (driving force) of the internal combustion engine or the electric motor, braking force is required from the vehicle when a driver releases the foot from an accelerator pedal or possibly further depresses a brake pedal. At this time, an increase in vehicle speed is reduced or prevented by the regenerative braking force of the electric motor, and electric power (regenerative energy) generated as a result of regenerative braking is supplied to the storage battery. As a result, the SOC of the storage battery increases.
Therefore, when the vehicle travels on a long downhill (that is, a section having a relatively long distance and a relatively large altitude difference), the SOC may reach the upper limit halfway on the downhill, and the SOC cannot be increased any more. This means that the effect of improvement in fuel consumption, which is obtained as a result of traveling on a downhill, increases as the difference between the upper limit of the SOC and the SOC at the start point of the downhill increases.
One of existing control apparatuses for a vehicle (hereinafter, referred to as existing apparatus) acquires the position of the vehicle, a destination, map information (road information), and the like, with the use of a navigation system, and determines a scheduled travel route and a down-grade section (downhill section) in the scheduled travel route on the basis of those pieces of information. The existing apparatus estimates the amount of electric power that is newly chargeable into the storage battery through regenerative braking in a period during which the vehicle travels on the determined down-grade section. When the estimated amount of chargeable electric power is larger than an ordinary management range, the existing apparatus expands the management range of the storage battery to an expanded management range. In addition, the existing apparatus controls the electric motor or the internal combustion engine or both such that the SOC of the storage battery is consumed to the lower limit of the expanded management range by the time the vehicle starts traveling on the down-grade section. Hereinafter, such control is referred to as support control.
Usually, map information (particularly, for example, information pertaining to the altitudes of the start point and end point of each road section or the gradient of each road section) that is stored in a navigation database of the navigation system is created on the basis of actual terrain data measured in advance. Therefore, there is a case where the altitude (or gradient) of a road on which the vehicle actually travels does not coincide with the altitude (or gradient) stored in the navigation database. For example, in the case of a road inside a tunnel, the actual altitude of the road is lower than the altitude stored in the navigation database. In the case of a road on bridge girders, the actual altitude of the road is higher than the altitude stored in the navigation database.
Thus, for example, even when a road inside a tunnel or a road on girders is actually a low-grade slope (or a no-grade flat road), the existing apparatus is likely to erroneously determine that the road is part of a downhill section and, as a result, execute unnecessary support control over a section that is originally not a slope.
For example, when the existing apparatus erroneously recognizes a section on which the vehicle will pass as part of a downhill section although the section is actually a flat road, the existing apparatus decreases the SOC such that the SOC approaches from a first target SOC to a second target SOC lower than the first target SOC by the time the vehicle reaches a point recognized as the start point of the downhill section. However, the vehicle actually travels on a flat road not on a downhill on that downhill section, so the SOC of the storage battery does not increase as expected and, on the contrary, reduces as a result of traveling on the flat road, and the SOC is likely to reach the lower limit of the management range. When the SOC reaches the lower limit of the management range, the existing apparatus starts the internal combustion engine in order to charge the storage battery, which is a cause of deterioration of the fuel consumption.
In contrast, when the existing apparatus erroneously recognizes a section on which the vehicle will pass as a flat road although the section is actually a downhill, the existing apparatus does not execute support control. Therefore, the SOC is not sufficiently decreased before the start point of the down grade, the existing apparatus is likely not to be able to recover regenerative energy that could have been originally recovered.